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Carb/Choke PLEASE HELP!!!!

Discussion in 'The Garage' started by BRN78BLAZER, Jun 24, 2003.

  1. BRN78BLAZER

    BRN78BLAZER 1/2 ton status

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    Location:
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    rebuilt 2bbl Rochestor on a HD emission 78 305

    choke thermostat(brand new) is mounted on the manifold and uses a rod to operate the choke.

    The problem - If I set it so that it starts and idles smoothly the fast idle stays on way too long, like 2 or 3 miles, at 80 + degrees. If I try backing it off, it is very hard to get running and idling smoothly in the morning,(when I say morning I still mean like 80 degrees) it will start, on high idle for a few sec. then slowly drop down and stall. starting it 3 or 4 times will gewt it idling very rough and lumpy at around 10 - 1200 rpm. it will idle smooth out after a min. of driving and be on high idle @ 1500 rpm, and come on to low idle after about 3/4 - 1 mile of driving, which I still think is too long for such 80 deg.

    In the winter it was fine. It would start on high idle, nice smooth, run it for 30 sec - 1 min, then drive it, and it would be on low idle after about 3/4 of a mile. Which to me seemed perfect. Then the warm weather came and thats when it started acting up. Am I wrong in thinking that it should stay on less in warmer weather????????

    I had a carb specialist set it, with no improvement. It will start and idle fine, but the fast idle stays on way too long. He said it has to be that way. I say bull sh**. My dads 79 350 qjet, in this weather starts on low idle runs fine, even in winterthe high idle will only stay on for not even 1/2 a mile, and it never hesitates, stumbles, or stalls. Smooth as glass.

    What do I need to do? Please help me! Everything as in plug wires cap, vacumm lines, compression,... pretty much evrything has been checked over and is in excellent shape.

    Im tempted to just replace it with a Q jet or similar 4 bbl, only mine is all original and I like it that way, and the fact that I may just run into more problems going that route.

    Please help- I'm stuck and very frustrated.

    Thanks in advance
    Steve
     
  2. BRN78BLAZER

    BRN78BLAZER 1/2 ton status

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    Has anyone ever experience similiar problems with the 2bbls?

    What I need is a way for it to come on more when you intitially start it, but then come off a lot sooner. At least I think that would solve it.
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    If we are dealing with the choke coil mounted on the intake (which we are), the way to get it to move sooner or later, is to adjust the metal rod linking the carb to the intake. Straightening it out gets FASTER (and more) travel at the carb, so it should come off faster, and open further (if that was an issue).

    Don't mess with it too much though, it is very easy to overdo the choke settings on these carbs.

    You may have to go back in and adjust high idle speed and such, but you have to do only one thing at a time, or you will be completely lost trying to get back to where you started if it doesn't work right.
     
  4. Blazer1970

    Blazer1970 1/2 ton status

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    Also, it is very common for the exhaust crossover in the intake to plug up, which means that not enough heat will get to the bimetal spring that opens the choke. It may be that in cold weather, the engine is just that much more tolerant of running with the choke partly closed (which it would be). It doesn't really jibe with your description of how the high idle is working though. I would pull the intake and check the crossover, and clean it out if necessary.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Isn't the intake crossover like 2" by 1" tall? I'm not saying it won't happen, but I've never seen one (or heard of it before) plugged up either.

    Of course, my dealings have been mostly with Oldsmobile, and their crossovers are that size, not sure on the Chev's.
     
  6. BRN78BLAZER

    BRN78BLAZER 1/2 ton status

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    For some reason I thought that Putting a bend in that rod it would come off faster. So I straightend it out, and I looked through a book in the library and it explained how to check and set that rod by bending the lever on the carb. As well as setting the vacumm pulloff.

    I think origionally I must have screwed it up by over adjusting it, then trying to compensate by adjusting more /forums/images/graemlins/crazy.gif. But it should be close now, although I won't know until morning. As for the crossover being plugged...I'm going to look into it but am going to research it first. Does that valve on the passenger side exhaust manifold have anything to do with it? Cause I think mine might be stuck open now that I think about it.

    Thanks alot so far guys, atleast I'm getting some new ideas /forums/images/graemlins/thumb.gif
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    That valve, when closed, forces the passenger side exhaust through the intake into the passenger side exhaust. Theoretically this heats up the intake faster, but should only occur when the engine is cold anyways.

    Not sure what kind of engine temp we are talking, but it should be fairly low. If it was diverting all the time, it would probably be sluggish as heck and you'd end up with extremely hard starts, since the carb would be getting hotter than it should.

    Besides the benefit of EGR, I think that way of heating the carb is pretty crummy, since the crossover is always open, you are always heating the carb up more than it needs. At least more than heat conducted from the intake and heads alone provides.
     

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